In a typical wireless, cellular or radio communications network, wireless devices, also known as mobile stations, terminals, and/or User Equipment, UEs, communicate via a Radio-Access Network, RAN, with one or more core networks. The RAN covers a geographical area which is divided into cells, with each cell being served by a base station, e.g. a radio base station, RBS, or network node, which in some networks may also be called, for example, a “NodeB”, “eNodeB” or “eNB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. One radio base station may serve one or more cells.
A Universal Mobile Telecommunications System, UMTS, is a third generation mobile communication system, which evolved from the second generation, 2G, Global System for Mobile Communications, GSM. The UMTS terrestrial radio-access network, UTRAN, is essentially a RAN using wideband code-division multiple access, WCDMA, and/or High-Speed Packet Access, HSPA, to communicate with user equipment. In a forum known as the Third Generation Partnership Project, 3GPP, telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN, as e.g. in UMTS, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller, RNC, or a base station controller, BSC, which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System, EPS, have been completed within the 3rd Generation Partnership Project, 3GPP, and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio-Access Network, E-UTRAN, also known as the Long-Term Evolution, LTE, radio access, and the Evolved Packet Core, EPC, also known as System Architecture Evolution, SAE, core network. E-UTRAN/LTE is a variant of a 3GPP radio-access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio base station nodes, e.g. eNodeBs in LTE, and the core network. As such, the Radio-Access Network, RAN, of an EPS has an essentially flat architecture comprising radio base station nodes without reporting to RNCs.
FIG. 1 illustrates the current standard EPC architecture of a wireless communications network. The EPC architecture, including all of its components and interfaces, is further described and defined in 3GPP TS 23.401, version 12.0.0. The current standard E-UTRAN architecture is further described and defined in e.g. 3GPP TS 36.300, version 12.0.0.
FIG. 2 illustrates the radio interface user and control plane protocol for E-UTRAN. The E-UTRAN radio interface user and control plane protocol consists of the following protocol layers and main functionalities.
Radio Resource Control, RRC (Control Plane Only)
The main function for control plane: broadcast of system information for both Non-Access Stratum, NAS, and Access Stratum, AS; paging; Radio Resource Control, RRC, connection handling; Allocation of temporary identifiers for the UE; Configuration of signaling radio bearer(s) for RRC connection; Handling of radio bearers; Quality-of-Service, QoS, management functions; Security functions including key management; Mobility functions (including UE measurement reporting and control of the reporting, handover, UE cell selection and reselection and control of cell selection and reselection); and NAS direct message transfer to/from the UE.
Packet Data Convergence Protocol, PDCP
There exists one PDCP entity for each radio bearer for the UE. PDCP is used for both control plane, i.e. RRC, and for user plane, i.e. user data received via GTP-U signaling. Main function for control plane is ciphering/deciphering and integrity protection. Main functions for user plane: ciphering/deciphering, header compression and decompression using Robust Header Compression, ROHC, and in-sequence delivery, duplicate detection and retransmission.
Radio Link Control, RLC
The RLC layer provides services for the PDCP layer and there exists one RLC entity for each radio bearer for the UE. Main functions for both control and user plane: segmentation/concatenation, retransmission handling, duplicate detection, and in-sequence delivery to higher layers.
Medium Access Control, MAC
The MAC provides services to the RLC layer in the form of logical channels, and performs mapping between these logical channels and transport channels. Main functions are: uplink and downlink scheduling, scheduling information reporting, Hybrid Automatic Repeat reQuest, HARQ, retransmissions, and multiplexing/de-multiplexing data across multiple component carriers for carrier aggregation.
Physical Layer, PHY
The PHY provides services to the MAC layer in the form of transport channels and handles mapping of transport channels to physical channels.
Information relating to one or more of these protocol layers and their functionality is hereinafter referred to as Radio Access Network, RAN, context information. In other words, the configuration of these protocol layers for a particular wireless device would be the RAN context information of this particular wireless device in the wireless communications network. The configuration of these protocol layers are typically done by on the RRC layer via RRC configuration messages. One example of configuration specific information is different identifiers on the different protocol layers for the wireless device. However, it should also be noted that the RAN context information may further include additional information, such as, for example, radio access capabilities of the wireless device, previous mobility or traffic history of the wireless device, etc.
The above described functionality of the network node, eNB, may be deployed in different ways. In one example, all the protocol layers and related functionality is deployed in the same physical node including the antenna. One example of this is a so-called Pico or Femto eNodeB. Another example is a so-called Main-Remote split. In this case, the eNodeB is divided into a main unit and a remote unit. The main unit may also be referred to as a Digital Unit, DU, and the remote unit also referred to as a Remote Radio Unit, RRU. In this case, the main unit comprises all the protocol layers, except the lower parts of the PHY layer that are instead placed in the remote unit. In a further example, remote unit and the antenna are co-located. This may be referred to as an Antenna Integrated Radio, AIR, system.